1. Field of the Invention
The present invention relates to a method of producing an information recording material, particularly to a method of producing, with good productivity, an information recording material such as a thermal recording material and an inkjet recording material excellent in various properties and excellent in coating qualities in particular.
2. Related Art Statement
Information recording materials having an information-recording layer formed on a substrate are used in broad fields. A variety of recording materials such as a pressure-sensitive recording material, a thermal recording material, a thermal transfer recording material, an inkjet recording material, etc., are practically used as such information recording materials. In recent years, information recording materials having two or more layers formed on a substrate are also used due to demands for higher functions and higher performances.
A thermal recording material is generally a material in which a heat-sensitive recording layer containing a thermally color-formable material is formed on a substrate. An image is formed by heating it with a thermal head, a thermal pen, laser light, or the like. The thermal recording material is disclosed in Japanese Patent Publications Nos. 43-4160, 45-14039 and the like.
The above thermal recording material is advantageous in that a recording can be obtained with a relatively simple unit, that maintenance is easy and that no noise is made, so that it is widely used in the fields of measuring recorders, facsimile machines, computer terminals, labels, automatic vending machines of tickets, etc. In recent years, further, for attaining superior color density and sensitivity, image stability and tones of a plurality of colors, there is practically used a thermal recording material prepared by applying a protective layer, an undercoat layer and two or more heat-sensitive recording layers, in addition to a thermal recording material having a single heat-sensitive recording layer alone.
An inkjet recording method is a method in which fine globules of an ink are ejected from an inkjet recording device and allowed to adhere to an inkjet recording material to form an image or letters. As the above inkjet recording material, a material having no ink receptor layer such as a non-coated paper is sometimes used. However, a material prepared by forming an ink receptor layer on a substrate is used when printing is made on a synthetic resin film having no ink-reception properties or when it is intended to obtain a finer image. With diversification in use, color imaging or higher performances such as faster printing in recent years, a larger amount of an ink is ejected, and a higher-capacity ink absorption and a higher print density come to be required. Since no sufficient performances for the above requirements can be obtained with any conventional single ink receptor layer, an inkjet recording material having two or more ink receptor layers are practically used as well.
In a conventional information recording material having two or more layers laminated on a substrate, each layer is independently formed by application and drying to form the laminated layers, and the application is carried out by a method such as an air knife coating method, a blade coating method, a rod coating method or a reverse roll coating method. However, an information recording material prepared by any one of the above methods has problems that its coating quality is poor, that an upper layer has pin holes caused by infiltration of an upper layer coating color into a lower layer and repellency during application to form the upper layer and that the quality varies due to continuous coating for a long period of time. Moreover, there are problems in a limit to application at a high rate and a decrease in productivity due to application procedures to be carried out a plurality of times.
As compared with these methods, the curtain coating method disclosed in Japanese Patent Publications Nos. 49-24133 and 49-35447 is an application method in which a free-fall curtain of a coating color is formed and allowed to collide with a substrate, and it is known that the curtain coating method is suitable for application at a high rate. Further, since a plurality of layers can be simultaneously formed by forming a coating composition film made of a plurality of coating color layers, the productivity in multi-layer application can be improved to a great extent. In the simultaneous multi-layer application using a curtain coating method, the coating composition film made of a plurality of coating color layers is formed on a substrate, and thereafter, it is required to dry the coating composition film to solidness without disordering the layer structure thereof. In the field of conventional photographic photosensitive materials prepared by simultaneous multi-layer application using a curtain coating method, each coating color contains gelatin as a binder, and coating composition layers are cooled immediately after coating composition solutions are transferred onto a substrate, so that the gelatin in the coating colors gelled and that the coating composition solution are immobilized, whereby no intermingling of the layers takes place.
Under the circumstances, it is an object of the present invention to provide a method of producing an information recording material having at least two layers laminated on a substrate, with good productivity, in which pinholes in an upper layer and the variability in coating qualities, caused by the infiltration of a coating color for the upper layer into a lower layer and repellency during application for forming the upper layer, are inhibited and the information recording material is excellent in coating qualities and are excellent in various properties.
The present inventors have therefore made diligent studies for achieving the above object, and as a result, it has been found that the above object can be achieved by forming a coating composition film made of a plurality of coating color layers on a substrate by curtain coating and drying the coating composition film to form part or all of layers for forming an information recording material, and either (1) by adjusting the viscosity of each of the coating colors for a plurality of the coating color layers to a certain value or above and controlling the surface tension of the coating color for a lowermost layer so as to bring it into a specific range or (2) by controlling the density of the coating color for each layer for forming a plurality of the coating color layers. The present invention has been completed on the basis of the above findings.
That is, (1) according to the present invention, there is provided a method of producing an information recording material having at least two layers laminated on a substrate, which comprises forming a coating composition film made of a plurality of coating color layers on a substrate by curtain coating and drying the coating composition film, to form part or all of layers for forming the information recording material, wherein the coating colors for a plurality of the coating color layers during application have a viscosity of at least 100 mPaxc2x7s and the coating color for a lowermost layer of a plurality of the coating color layers has a surface tension of 18 to 45 mN/m (to be referred to as xe2x80x9cProduction method I of the present inventionxe2x80x9d hereinafter).
(2) According to the present invention, there is also provided a method of producing an information recording material having at least two layers laminated on a substrate, which comprises forming a coating composition film made of a plurality of coating color layers on a substrate by curtain coating and drying the coating composition film, to form part or all of layers for forming the information recording material, wherein a coating color for a layer to be positioned above has a density which does not exceed 140% of the density of a coating color for a layer to be positioned below and adjacent thereto (to be referred to as xe2x80x9cProduction method II of the present inventionxe2x80x9d hereinafter).
The method of producing an information recording material according to the present invention includes two modes. The Production method I of the present invention will be explained first.
In the Production method I, part or all of the layers for forming an information recording material are formed by forming a coating composition film made of a plurality of coating color layers on a substrate by a curtain coating and drying the coating composition film.
Production method I is suitably used for producing a thermal recording material as an information recording material. While the layers formed by curtain coating are not specially limited in kind, the layers include an undercoat layer, a heat-sensitive recording layer, a protective layer, etc., and a series of these adjacent layers are simultaneously applied in the form of multi-layers by curtain coating. Specific examples of the combination of layers to be formed by simultaneous application in the form of multi-layers include a combination of an undercoat layer and a heat-sensitive recording layer, a combination of a heat-sensitive recording layer and a protective layer, a combination of an undercoat layer, a heat-sensitive recording layer and a protective layer, and some other combination. Further, these combinations include a combination of undercoat layers of two or more different kinds, a combination of heat-sensitive recording layers of two or more different kinds, a combination of protective layers of two or more different kinds, etc., although these combinations are not critical.
In Production method I of the present invention, coating colors for the above layers are adjusted to a viscosity of at least 100 mPaxc2x7s for preventing intermingling of layers during the curtain coating. The viscosity of each coating color refers to a value measured with a Brookfield viscometer at a temperature during the application. When coating colors adjusted to the above viscosity are simultaneously applied in the form of multi-layers by a curtain coating method, intermingling of layers is decreased, and there can be formed layers each of which has excellent coating qualities such as a uniform thickness and freedom from occurrence of pinholes, as compared with a case where the layers are formed one by one by a conventional method such as an air knife coating method, a blade coating method, a rod coating method or a reverse roll coating method and dried to form a laminate. When the viscosity of the coating colors is less than 100 mPaxc2x7s, intermingling of layers is liable to take place when the coating composition film in the form of a curtain collides with a substrate or during the drying of the coating composition film transferred onto the substrate. After the coating composition film is dried, inter-layer separation or the laminated state of the layers is poor, so that the functions of the layers cannot be sufficiently exhibited. Further, the infiltration of a layer into the substrate or a layer which is formed below the layers to be formed by curtain coating increases, so that the inter-layer separation or the laminated state of the layers is deteriorated. With an increase in the viscosity of each coating color, intermingling of layers decreases so that the inter-layer separation comes to be superior. When the viscosity of each coating color is too high, the viscous force is too high, a point where the coating composition film arrives onto a substrate shifts toward a downstream side with regard to the running direction of the substrate, and an air layer enters between the substrate and the coating composition film, so that the state of application is destabilized in some cases. Particularly preferably, the viscosity of each coating colors is at least 100 mPaxc2x7s and does not exceed 2,000 mPaxc2x7s. Further, intermingling of layers is decreased as the viscosity difference between/among the coating colors to be applied by curtain coating for forming the layers decreases, and preferably, the viscosity difference between/among the coating colors is 100 mPaxc2x7s or less.
In the Production method I, further, the surface tension of the coating color for the lowermost layer of the layers to be applied by curtain coating is adjusted to 18 to 45 mN/m. The surface tension of the lowermost layer has an influence on easiness in transfer of the coating composition film onto a substrate. This surface tension of a coating color refers to a value measured with a tensiometer using a platinum ring at a temperature of the coating color during its application. With a decrease in the surface tension of the coating color for the lowermost layer, the coating composition film is more easily transferred onto a substrate, and the coating composition film can be applied at a higher rate. When the above surface tension is smaller than 18 mN/m, the infiltration into a substrate or a layer formed below the layer to be applied by curtain coating increases, which may deteriorate a layer-separated and laminated state. When the surface tension is greater than 45 mN/m, it is difficult to transfer the coating composition film onto a substrate, so that the application may be impossible, or that, even if the application is possible, no information recording material having good coating quality cannot be obtained in some cases. When the surface tension of the coating color for the lowermost layer is adjusted to 20 to 45 mN/m, desirably, the easiness in the transfer of the coating composition film onto a substrate and the difficulty in infiltration of the lowermost layer into the substrate are well balanced. This surface tension is preferably in the range of 20 to 40 mN/m.
It is particularly preferred to arrange the surface tensions of the coating colors such that layer(s) for forming upper layer(s) have a smaller surface tension than layer(s) for forming lower layer(s), since an information recording material having superior coating quality can be obtained. When a coating color for forming a lower layer has a smaller surface tension than a coating color for forming an upper layer, there is caused a phenomenon that the coating color forming the upper layer is repelled on the coating color forming the lower layer, no uniform coating composition film is formed, and an information recording material is poor in coating quality. When three or more layers are applied simultaneously, it is preferred to arrange the surface tensions of the layers such that the surface tensions gradually decrease from the lowermost layer, i.e., the layer closest to a substrate to the uppermost layer farthest from the substrate.
Although not specially limited, an applicator machine for forming the coating composition film made of a plurality of coating color layers and transferring it onto a substrate includes an extrusion hopper type curtain coater and a slide hopper type curtain coater. The slide hopper type curtain coater disclosed in Japanese patent Publication No. 49-24133, which is used with a photographic photosensitive material, etc., is particularly preferably used. This slide hopper type curtain coater makes it easier to carry out simultaneous multi-layer application.
The viscosities of the coating colors can be adjusted to ranges specified in the present invention, for example, by a method in which a water-soluble polymer such as polyvinyl alcohol, starch or carboxymethyl cellulose or a thickener such as an acrylic emulsion is mixed with a coating color to increase its viscosity, a method in which a solid content in a coating color is increased to increase its viscosity, or a method in which a coating color is diluted to decrease its viscosity.
The surface tensions of the coating colors can be adjusted to the ranges specified in the present invention, for example, by a method in which a coating color is mixed with a proper amount of an anionic surfactant such as a carboxylic acid salt, a sulfonic acid salt, a sulfate or a phosphate, a nonionic surfactant such an ether type, an ether ester type, an ester type or a nitrogen-containing nonionic surfactant or an amphoteric surfactant such as betaine, an aminocarboxylic acid salt or an imidazoline derivative.
In the coating composition film made of a plurality of coating color layers applied onto a substrate with a curtain coater in the Production method I of the present invention, preferably, the density of the coating color for a layer to be positioned above does not exceed 140% of the density of the coating color for a layer to be positioned below and adjacent thereto. The density refers to a value at a temperature of the coating color during the application thereof. The layer to be positioned above and the layer to be positioned below are under on condition in a drying step following the curtain coating of the coating composition film on a substrate.
The coating composition film formed on a substrate by curtain coating gradually proceeds with intermingling of layers immediately after its application. When a coating color for a layer to be positioned above has a larger density than a coating color for an adjacent layer to be positioned below, the coating color for a layer to be positioned above infiltrates the adjacent layer to be positioned below, so that the intermingling of layers is promoted. In particular, when the density of the coating color for a layer to be positioned above exceeds 140% of the density of the coating color for an adjacent layer to be positioned below, the intermingling of layers takes place to an extreme extent, and the functions of the layers constituting an information recording material may be lost in some cases.
When the density of the coating color for a layer to be positioned above exceeds 100% of the density of the coating color for an adjacent layer to be positioned below but does not exceed 140% thereof, the intermingling of layers is promoted to some extent, but sufficient functions of the layers constituting an information recording material can be obtained. Further, when the density of the coating color for a layer to be positioned above is 100% of the density of the coating color for an adjacent layer to be positioned below, desirably, no intermingling of layers caused by a density difference between coating colors takes place. Further, when the density of the coating color for a layer to be positioned above is less than 100% of the density of the coating color for an adjacent layer to be positioned below, particularly desirably, the action of preventing the intermingling of layers is exhibited.
The method of adjusting the density of the coating color for each layer as described above is not specially limited. Specific examples include a method in which the concentration of a coating color is adjusted, a method in which a component having a high density is incorporated into a coating color and a method in which a liquid component which is volatilized in a drying step following the application is incorporated into a coating color.
In the relationship of a substrate with a layer to be positioned above and a layer to be positioned below of a plurality of the coating color layers, a layer closer to the substrate is taken as a layer to be positioned below, and a layer farther from the substrate is taken as a layer to be positioned above. In this case, the coating composition film can be dried in a state where the coating composition film is positioned on an upper side of the substrate, so that an information recording material can be more easily produced. Due to some limitation to the coating color of a layer to be applied, it is difficult to take a layer closer to the substrate as a layer to be positioned below and to take a layer farther from the substrate as a layer to be positioned above in some cases. In such cases, the coating composition film may be dried in a state where the coating composition film is on the lower side of the substrate such that a layer closer to the substrate is a layer to be positioned above and that a layer farther from the substrate is a layer to be positioned below.
In the Production method I of the present invention, preferably, the coating composition film made of a plurality of the coating color layers formed on a substrate with a curtain coater is dried within 2 minutes after its application. The term xe2x80x9cdryingxe2x80x9d means that water or an organic solvent contained in coating colors forming the coating composition film is evaporated so that the fluidity of the coating colors is substantially removed. In the coating composition film formed on a substrate by curtain coating, intermingling of layers gradually proceeds immediately after its application. If it takes a longer time to dry the coating composition film after its application, the intermingling of layers takes to a great extent, and when the drying takes more than 2 minutes after the application, it is difficult to obtain an information recording material excellent in various properties in some cases. For example, in a thermal recording material, an undercoat layer and a heat-sensitive recording layer are simultaneously applied in the form of multi-layers by curtain coating, and if the drying takes more than 2 minutes, there may be caused a state where the undercoat layer and the heat-sensitive recording layer are intermingled, so that the color density may be low. Further, a heat-sensitive recording layer and a protective layer are simultaneously applied in the form of multi-layers by curtain coating, and if the drying takes more than 2 minutes, there may be caused a state where the heat-sensitive recording layer and the protective layer are intermingled so that there may be caused a problem that the barrier properties of the protective layer are low or that defective printing occurs. In an inkjet recording material, intermingling of a plurality of recording layers causes a decrease in color density and a decrease in ink absorption and absorption rate. When the drying takes more than 2 minutes after the application, intermingling of layers is liable to take place, and the function of each layer may not be fully exhibited. When the drying is completed within 2 minutes after the application, the intermingling of layers rarely takes place, the function of each layer can be fully exhibited, and there can be obtained an information recording material excellent in various properties. As the time period required for completion of the drying decreases, there can be obtained an information recording material more excellent in various properties.
The drying method is not critical. Specifically, the drying method includes a method in which hot air is blown, a method in which dehumidified air is blown, a method in which infrared rays are used for irradiation and a method in which microwaves are used for irradiation. Some of these methods may be used in combination.
Of the above drying methods, in the method using hot air blowing or a dehumidified air blowing, the layer structure of the coating color layers forming the coating composition film may be disordered due to an impact of air blown thereto, so that it is preferred to decrease the impact of air blowing so as to make it as small as possible. For decreasing the impact of air blowing, and for completing the drying for a short period of time after the application, essentially, air is heated to a sufficiently high temperature when hot air is used, and water is fully removed from dehumidified air when dehumidified air is used.
Of the above drying methods, the method using infrared rays for irradiation and the method using microwaves for irradiation are preferably used since no impact is exerted on an applied coating composition film. The method using hot air blowing, the method using dehumidified air blowing and the method using irradiation with infrared rays are disadvantageous to some extent in view of maintaining the stability of layer structure of the coating color layers forming the coating composition film, since the drying of a coating composition film surface proceeds earlier than the drying of the interior thereof. The method using irradiation with microwaves is particularly preferred since both the surface and the interior of the coating composition film can be wholly simultaneously dried so that the layer structure of the coating color layers forming the coating composition film is hardly disordered.
In Production method I of the present invention, preferably, the coating composition film made of a plurality of coating color layers formed on a substrate with a curtain coater is dried in a state where an angle formed by the substrate and a horizontal plane is 45 degrees or less. The above angle formed by the substrate and a horizontal plane refers to a gradient of the substrate to the horizontal plane. 0 Degree shows that the substrate is in parallel with the horizontal plane, and 90 degrees shows that the substrate exists in a plane perpendicular to the horizontal plane. In this case, it is not critical whether the coating composition film is formed on the upper side or lower side of the substrate.
In the coating composition film formed on a substrate by curtain coating, intermingling of layers gradually proceeds immediately after its application until the drying is completed, as already described. It is therefore required to carry out the drying in a state where the intermingling of layers hardly proceeds immediately after the application until completion of the drying. When a substrate is inclined with regard to the horizontal plane, the coating composition film applied onto the substrate is liable to flow toward a lower side along the substrate in parallel with the substrate due to gravity. When the coating composition film made of a plurality of coating color layers flows along a substrate, the flow rate may differ from one layer to another due to a viscosity difference among layers, the flow rate of a layer closer to the substrate may differ from the flow rate of a layer father from the substrate due to a friction with the substrate, and the layer structure of the coating composition film may be therefore disordered, so that the intermingling of layers may occur. In the drying method using hot air blowing, the drying proceeds earlier on the coating composition film surface, and there is therefore caused a large difference in the viscosity distribution in the coating composition film, so that a large difference is caused in flow rates and that the intermingling of layers is promoted. It is therefore difficult to obtain an information recording material excellent in various properties. For example, in a thermal recording material, an undercoat layer and a heat-sensitive recording layer are simultaneously applied in the form of multi-layers by curtain coating, and if the undercoat layer and the heat-sensitive recording layer are intermingled, the color density is low. A heat-sensitive layer and a protective layer are simultaneously applied in the form of multi-layers by curtain coating, and if the heat-sensitive recording layer and the protective layer are intermingled, the barrier properties of the protective layer are low or that defective printing occurs. In an inkjet recording material, intermingling of a plurality of ink receptor layers causes a decrease in color density and a decrease in ink absorption and absorption rate. When layers are intermingled as described above, it is difficult to allow each layer to exhibit its full functions.
The above intermingling of layers caused by the flow of coating composition film increases with an increase in the gradient of the substrate, so that the intermingling of the layers can be prevented by drying the coating composition film in a state where the substrate is so positioned as to be as horizontal as possible. When the coating composition film is dried in a state where the angle formed by the substrate and the horizontal plane is 45 degrees or less, the intermingling of layers can be prevented to such an extent that the properties of an information recording material are not impaired. Further, when the coating composition film is dried in a state where the angle formed by the substrate and the horizontal plane is 20 degrees or less, particularly preferably, there can be obtained an information recording material nearly as excellent in properties as that obtained by carrying out the drying in a state where the substrate is in a completely horizontal state.
The method of the above drying is not critical. Specifically, the drying method includes a method in which hot air is blown, a method in which dehumidified air is blown, a method in which infrared rays are used for irradiation and a method in which microwaves are used for irradiation. Some of these methods may be used in combination.
Production method II of the present invention will be explained hereinafter.
In Production method II of the present invention, part or all of the layers for forming an information recording material are formed by forming a coating composition film made of a plurality of coating color layers on a substrate by a curtain coating and drying the coating composition film.
Production method II is suitably used for producing a thermal recording material or an inkjet recording material as an information recording material. The layers to be formed by curtain coating are not specially limited. For example, the layers for a thermal recording material include an undercoat layer, a heat-sensitive recording layer and a protective layer. The layers for an inkjet recording material include a plurality of ink receptor layers. A series of these adjacent layers are simultaneously applied in the form of multi-layers by curtain coating. Specific examples of the combination of layers to be formed by simultaneous application in the form of multi-layers include a combination of an undercoat layer and a heat-sensitive recording layer, a combination of a heat-sensitive recording layer and a protective layer, a combination of an undercoat layer, a heat-sensitive recording layer and a protective layer, and some other combination. Further, these combinations include a combination of undercoat layers of two or more different kinds, a combination of heat-sensitive recording layers of two or more different kinds, a combination of protective layers of two or more different kinds, etc. The combination in an inkjet recording material includes a combination of a plurality of ink receptor layers. These combinations are not critical.
The curtain coater for forming the coating composition film made of a plurality of coating color layers on a substrate by curtain coating can be selected from those explained with regard to Production method I of the present invention.
In the coating composition film made of a plurality of coating color layers applied onto a substrate with a curtain coater in the Production method II of the present invention, the density of the coating color for a layer to be positioned above does not exceed 140% of the density of the coating color for a layer to be positioned below and adjacent thereto. The above density refers to a value at a temperature of the coating color during the application thereof. The layer to be positioned above and the layer to be positioned below have the same meanings as those explained in Production method I.
The coating composition film formed on a substrate by curtain coating gradually proceeds with intermingling of layers immediately after its application. When a coating color for a layer to be positioned above has a larger density than a coating color for an adjacent layer to be positioned below, the coating color for a layer to be positioned above infiltrates the adjacent layer to be positioned below, so that the intermingling of layers is promoted. In particular, when the density of the coating color for a layer to be positioned above exceeds 140% of the density of the coating color for an adjacent layer to be positioned below, the intermingling of layers takes place to an extreme extent, and the functions of the layers constituting an information recording material may be lost. When the density of the coating color for a layer to be positioned above exceeds 100% of the density of the coating color for an adjacent layer to be positioned below but does not exceed 140% thereof, the intermingling of layers is promoted to some extent, but sufficient functions of the layers constituting an information recording material can be obtained. Further, when the density of the coating color for a layer to be positioned above is 100% of the density of the coating color for an adjacent layer to be positioned below, desirably, no intermingling of layers caused by a density difference between coating colors takes place. Further, when the density of the coating color for a layer to be positioned above is less than 100% of the density of the coating color for an adjacent layer to be positioned below, particularly desirably, the action of preventing the intermingling of layers is exhibited.
The method of adjusting the density of the coating color for each layer as described above includes those methods explained in Production method I.
In the relationship of a substrate with a layer to be positioned above and a layer to be positioned below of a plurality of the coating color layers, a layer closer to the substrate is taken as a layer to be positioned below, and a layer farther from the substrate is taken as a layer to be positioned above. In this case, the coating composition film can be dried in a state where the coating composition film is positioned on an upper side of the substrate, so that an information recording material can be more easily produced. Due to some limitation to the coating color of a layer to be applied, it is difficult to take a layer closer to the substrate as a layer to be positioned below and to take a layer farther from the substrate as a layer to be positioned above in some cases. In such cases, the coating composition film may be dried in a state where the coating composition film is on the lower side of the substrate such that a layer closer to the substrate is a layer to be positioned above and that a layer farther from the substrate is a layer to be positioned below.
In Production method II of the present invention, preferably, coating colors for the above layers are adjusted to a viscosity of at least 100 mPaxc2x7s for preventing intermingling of layers during the curtain coating. The viscosity of each coating color refers to a value measured with a Brookfield viscometer at a temperature during the application. When coating colors adjusted to the above viscosity are simultaneously applied in the form of multi-layers by a curtain coating method, intermingling of layers is decreased, and there can be formed layers each of which has excellent coating qualities such as a uniform thickness and freedom from occurrence of pinholes, as compared with a case where the layers are formed one by one by a conventional method such as an air knife coating method, a blade coating method, a rod coating method or a reverse roll coating method and dried to form a laminate. When the viscosity of the coating colors is less than 100 mPaxc2x7s, intermingling of layers is liable to take place when the coating composition film in the form of a curtain collides with a substrate or during the drying of the coating composition film transferred onto the substrate. After the coating composition film is dried, inter-layer separation or the laminated state of the layers is poor, so that the functions of the layers cannot be sufficiently exhibited. Further, the infiltration of a layer into the substrate or a layer which is formed below the layers to be formed by curtain coating increases, so that the inter-layer separation or the laminated state of the layers may be deteriorated. With an increase in the viscosity of each coating color, intermingling of layers decreases so that the inter-layer separation comes to be superior. When the viscosity of each coating color is too high, the viscous force is too high, a point where the coating composition film arrives onto a substrate shifts toward a downstream side with regard to the running direction of the substrate, and an air layer enters between the substrate and the coating composition film, so that the state of application is destabilized in some cases. Particularly preferably, the viscosity of each coating colors is at least 100 mPaxc2x7s and does not exceed 2,000 mPaxc2x7s. Further, intermingling of layers is decreased as the viscosity difference between/among the coating colors to be applied by curtain coating for forming the layers decreases, and preferably, the viscosity difference between/among the coating colors is 100 mPaxc2x7s or less.
In the Production method II, further, the surface tension of the coating color for the lowermost layer of the layers to be applied by curtain coating is preferably adjusted to 18 to 45 mN/m. The surface tension of the lowermost layer has an influence on easiness in transfer of the coating composition film onto a substrate. This surface tension of a coating color refers to a value measured with a tensiometer using a platinum ring at a temperature of the coating color during its application. With a decrease in the surface tension of the coating color for the lowermost layer, the coating composition film is more easily transferred onto a substrate, and the coating composition film can be applied at a higher rate. When the above surface tension is smaller than 18 mN/m, the infiltration into a substrate or a layer formed below the layer to be applied by curtain coating increases, which may deteriorate a layer-separated and laminated state. When the surface tension is greater than 45 mN/m, it is difficult to transfer the coating composition film onto a substrate, so that the application may be impossible, or that, even if the application is possible, no information recording material having good coating quality cannot be obtained in some cases. When the surface tension of the coating color for the lowermost layer is adjusted to 20 to 45 mN/m, more desirably, the easiness in the transfer of the coating composition film onto a substrate and the difficulty in infiltration of the lowermost layer into the substrate are well balanced. This surface tension is preferably in the range of 20 to 40 mN/m.
It is particularly preferred to arrange the surface tensions of the coating colors such that layer(s) to be positioned above have a smaller surface tension than layer(s) to be positioned below, since an information recording material having superior coating quality can be obtained. When a coating color for a layer to be positioned below has a smaller surface tension than a coating color for a layer to be positioned above, there is caused a phenomenon that the coating color layer forming the layer to be positioned above is repelled on the coating color layer forming the layer to be positioned below, no uniform coating composition film is formed, and an information recording material is poor in coating quality. When three or more layers are applied simultaneously, it is preferred to arrange the surface tensions of the layers such that the surface tensions gradually decrease from the lowermost layer, i.e., the layer closest to a substrate to the uppermost layer farthest from the substrate.
The viscosities and surface tensions of the coating colors are adjusted as explained in Production method I.
In the Production method II of the present invention, preferably, the coating composition film made of a plurality of coating color layers formed on a substrate with a curtain coater is dried within 2 minutes after its application like Production method I. The drying is carried out by the method explained in Production process I.
In the Production method II of the present invention, preferably, the coating composition film made of a plurality of coating color layers formed on a substrate with a curtain coater is dried in a state where an angle formed by the substrate and a horizontal plane is 45 degrees or less, like Production method I. The drying is carried out by the method explained in Production method I.
The most preferred embodiment of the method of producing an information recording material, provided by the present invention, satisfies the following requirements (1) to (4) when part or all of the layers for forming an information recording material are formed by forming a coating composition film made of a plurality of coating color layers on a substrate by a curtain coating and drying the coating composition film.
(1) The coating colors for a plurality of the above coating color layers have a viscosity of at least 100 mPaxc2x7s during application, and the coating color for the lowermost layer of a plurality of the coating color layers has a surface tension of 18 to 45 mN/m.
(2) The coating color for a layer for forming an upper layer of a plurality of the coating color layers has a density which does not exceed 140% of the density of the coating color for a layer for forming an adjacent lower layer.
(3) The coating composition film made of a plurality of the coating color layers is dried within 2 minutes after it is formed on a substrate.
(4) The coating composition film made of a plurality of the coating color layers is dried in a state where the angle formed by the substrate and a horizontal plane is 45 degrees or less.
In the Production methods (I and II) of the present invention, the coating colors of a plurality of the coating color layers forming the coating composition film to be formed on a substrate may contain additives as required. The additives include a pigment dispersing agent, a thickener, a fluidity improver, an anti-foaming agent, a foaming preventing agent, a release agent, a foaming agent, a penetrating agent, a coloring dye, a coloring pigment, a fluorescent brightener, an antioxidant, an antiseptic, a preservative, a water resistance imparting agent, a wet strength agent and a dry strength agent.
Each of the layers of the information recording material produced by the production method of the present invention may contain a binder as required. Specific examples of the binder include starches, hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxylmethyl cellulose, gelatin, casein, polyvinyl alcohol, modified polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polyacrylic ester, polymethacrylic ester, sodium polyacrylate, polyethylene terephthalate, polybutylene terephthalate, chlorinated polyether, an allyl resin, a furan resin, a ketone resin, oxybenzoyl polyester, polyacetal, polyether ether ketone, polyether sulfone, polyimide, polyamide, polyamideimide, polyaminobismaleimide, polymethyl pentene, polyphenylene ether, polyphenylene sulfide, polyphenylene sulfone, polysulfone, polyallylate, polyallyl sulfone, polybutadiene, polycarbonate, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyurethane, a phenolic resin, a urea resin, a melamine resin, a melamine-formalin resin, a benzoguanamine resin, a bismaleimide triazine resin, an alkyd resin, an amino resin, an epoxy resin, an unsaturated polyester resin, a styrene/butadiene copolymer, an acrylonitrile/butadiene copolymer, a methyl acrylate/butadiene copolymer, an ethylene/vinyl acetate copolymer, an acrylic amide/acrylic ester copolymer, an acrylic amide/acrylic ester/methacrylic acid terpolymer, an alkali salt of a styrene/maleic anhydride copolymer, an alkali salt or ammonium salt of an ethylene/maleic anhydride copolymer, and other polyolefin-containing resin. These binders may be used alone or in combination.
The substrate for the information recording material to be produced by the method of producing an information recording material, provided by the present invention, may be transparent, semi-transparent or non-transparent. The substrate includes paper, various non-woven fabrics, woven fabrics, a synthetic resin film, a synthetic resin laminated paper, a synthetic paper, a metal foil, a seramic paper, a glass sheet and composite sheets prepared by combining these, although the substrate shall not be limited thereto. These substrates are used depending upon purposes.
In the information recording material produced by the method of producing an information recording material, provided by the present invention, any layer thereof may contain inorganic and organic pigments such as diatomaceous earth, talc, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide and a urea-formalin resin; higher fatty acid metal salts such as zinc stearate and calcium stearate; waxes such as paraffin, paraffin oxide, polyethylene, polyethylene oxide, stearic acid amide and castor wax, a dispersing agents such as sodium dioctylsulfosuccinate; a surfactant; and a fluorescent dye.
For improving the information recording material in light resistance, an antioxidant and an ultraviolet absorbent may be incorporated. Examples of the antioxidant include a hindered-amine-containing antioxidant, a hindered-phenol-containing antioxidant and a sulfide-containing antioxidant, although the antioxidant shall not be limited thereto. Examples of the ultraviolet absorbent include organic ultraviolet absorbents such as a benzotriazole-containing ultraviolet absorbent, a salicylic-acid-containing ultraviolet absorbent and a benzophenone-containing ultraviolet absorbent, and inorganic ultraviolet absorbents such as zinc oxide, titanium oxide and cerium oxide, although the ultraviolet absorbent shall not be limited thereto.
A thermal recording material produced according to the method of producing an information recording material, provided by the present invention, contains components which form a color under heat. These components are not critical. For example, the components include a combination of a generally colorless or light-colored electron-donating dye precursor with an electron-accepting compound, a combination of an aromatic isocyanate compound with an imino compound, a combination of a generally colorless or light-colored electron-donating dye precursor with an aromatic isocyanate compound, a combination of a metallic compound with a coordination compound and a combination of a diazonium salt with a coupler. In view of excellence in various properties such as color formability and image stability, it is particularly preferred to use a combination of a generally colorless or light-colored electron-donating dye precursor with an electron-accepting compound, a combination of an aromatic isocyanate compound with an imino compound or a combination of a generally colorless or light-colored electron-donating dye precursor with an aromatic isocyanate compound.
In the thermal recording material produced by the method of producing an information recording material, provided by the present invention, any layer of the thermal recording material may contain a material capable of electrically, magnetically or optically recording information. A surface provided with a heat-sensitive recording layer or a surface opposite thereto may be imparted with the capability of receiving an inkjet recording ink. Further, a surface opposite to a surface provided with a heat-sensitive recording layer may be provided with a back-coating layer for preventing curling or electrostatic charge, and further, this surface may be processed to impart it with adhesiveness. Further, printing with a UV ink, etc., may be carried out on the surface of a heat-sensitive recording layer.
In the thermal recording material produced according to the method of producing an information recording material, provided by the present invention, any layer of the thermal recording material and its substrate may contain a light-heat converting material for printing with laser light.
In an inkjet recording material produced according to the method of producing an information recording material, provided by the present invention, any layer of the inkjet recording material may contain a material capable of electrically, magnetically or optically recording information. Further, a surface opposite to a surface provided with a ink receptor layer may be provided with a back-coating layer for preventing curling or electrostatic charge, and further, this surface may be processed to impart it with adhesiveness.
According to the present invention, infiltration of a coating color for an upper layer into a lower layer, a pinhole caused in an upper layer due to repellency during the application of a coating color for the upper layer and the variability in coating qualities are prevented when an information recording material having at least two layers laminated on a substrate is produced. An information recording material, such as a thermal recording material or an inkjet recording material, which is excellent in coating qualities and excellent in various properties, can be produced.